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Sept. 28, 2011 -- Having even slightly high blood pressure may substantially increase a person’s risk of having a stroke, new research shows.

The research, a review of 12 studies that included more than half a million people, found that adults who had prehypertension -- meaning systolic blood pressure (the top number) between 120 and 139 or diastolic blood pressure (the bottom number) between 80 and 89 -- had a 55% increased risk of having a stroke compared to adults whose blood pressure fell within the normal range.

According to the American Heart Association, blood pressure is the most powerful determinant of a person’s stroke risk.

Researchers have long observed that people with normal blood pressure have about half the risk of having a stroke over the course of their lives as those who have high blood pressure. But it was less clear what having prehypertension might mean for heart and blood vessel health , or whether it should even be treated.

“Across the board, whether we looked at race, ethnicity, or sex, there was this higher risk of stroke if you were diagnosed with prehypertension,” says researcher Bruce Ovbiagele, MD, a neuroscience professor and director of the Stroke Center at the University of California at San Diego.

The risks associated with prehypertension were even higher, however, for young and middle-aged adults, and for those who fell in the upper end of the prehypertensive range.

The study found that adults younger than 65 with prehypertension had a 68% increased risk of stroke. And those with a systolic blood pressure between 130 and 139 or a diastolic blood pressure between 85 and 89 had a nearly 80% increased risk of stroke.

Prehypertension didn’t increase the risk of stroke risk in seniors, probably because many adults who reach that age have other risk factors, including age and related health conditions, that come into play.

“It was interesting to confirm that there is this higher risk, but it was even more interesting to be able to narrow it down to certain types of individuals who seem to be at exceptionally high risk of having a stroke if they have prehypertension,” Ovbiagele says.

The study is published in the journal Neurology.

Does Higher-Than-Normal Blood Pressure Need Drug Treatment?

Experts who were not involved in the study called its findings compelling and said they may ultimately shift the threshold that doctors use to decide when to put their patients on blood-pressure-lowering drugs.

“It really makes us wonder whether we should be prescribing medications for those individuals,” says Amytis Towfighi, MD, assistant professor of neurology at University of Southern California in Los Angeles and chair of the neurology department at Rancho Los Amigos National Rehabilitation Center in Downey, Calif.

“However, to know for sure, we’d have to do a study to see if prescribing medications will actually lower stroke risk for those individuals,” says Towfighi, who wrote an editorial on the study.

Current guidelines don’t recommend medication for people with slightly elevated blood pressure unless they also have other health conditions like diabetes or chronic kidney disease.

Study researchers say that lifestyle changes are the best place to start when blood pressure numbers creep up into the prehypertension range.

Lifestyle changes that have been shown to lower blood pressure include cutting back on sodium and losing weight. “Lifestyle changes are very, very difficult, but if they’re done properly, we know that they work,” says Ovbiagele. “As a physician, I still think the best way to go is to modify one’s lifestyle.

“We know that prehypertension is rising with the obesity epidemic. I see patients who are 17, 18, and 19 who are having strokes, and they are almost exclusively obese. So I think something is going on and lifestyle changes could have an impact, albeit modest.”

That’s the advice Ovbiagele gives to his patients, but he knows that it may be difficult to make the changes necessary to get their blood pressure down to normal.

So he’s in the midst of designing his next study, which will test whether blood-pressure-lowering medications reduce stroke risk when they’re given to treat adults younger than 65 with blood pressures over 130/85.

One previous, small study did show that medication, when given for blood pressures in the prehypertensive range, were relatively safe and effective at preventing people from going on to develop full-blown high blood pressure (hypertension). The study did not follow patients to see if the aggressive therapy was able to lower a person’s risk for having a heart attack or stroke.